This invention relates to apparatus for confining the movement of animals, and particularly to apparatus for limiting the range of movement of an animal to a space within a defined boundary.
In one known approach to discouraging an animal from leaving a prescribed area, an aversive stimulus such as an electric shock is delivered to the animal whenever the animal approaches the perimeter of the prescribed area. One sort of apparatus for this approach includes a radio transmitter and a radio frequency receiver, carried by the animal, that includes electrodes for delivering an electric shock to the animal'skin; electronic circuitry in the receiver causes delivery of the electric shock in response to a signal from the transmitter. The transmitter can be configured to send the signal through a closed wire loop, which can be arranged about the perimeter of the prescribed area to form a so-called "invisible fence". Whenever the animal approaches within the field surrounding the wire loop, the receiver is triggered to deliver the aversive shock, from which the animal escapes by returning to within the prescribed area.
Radio frequency interference from a variety of sources in and around the domestic site can trigger the aversive shock stimulus, causing needless discomfort to the animal and breaking down the animal's specific conditioned response to the perimeter wire, compromising the effectiveness of the apparatus.